Nagai M, Nagai T, Yamamoto M, Goto K, Bishop T R, Hayashi N, Kondo H, Seyama Y, Kano K, Fujita H, Sassa S
Rockefeller University, New York, NY 10021, USA.
Biochem Pharmacol. 1997 Mar 7;53(5):643-50. doi: 10.1016/s0006-2952(96)00871-4.
The mode of expression of delta-aminolevulinate synthase (ALAS), as well as that of mRNAs for other heme pathway enzymes, was examined in the rat Harderian gland. Northern blot and in situ hybridization analyses demonstrated that the non-specific ALAS (ALAS-N) mRNA is highly expressed in this tissue, whereas the erythroid-specific ALAS (ALAS-E) mRNA is not. Immunoblot analysis of ALAS also confirmed this finding at the protein level. ALAS-N mRNA was maximally induced in the Harderian gland and was not increased further by treatment of animals with 2-allyl-2-isopropylacetamide (AIA). The levels of mRNAs for other heme pathway enzymes, i.e., delta-aminolevulinate dehydratase, porphobilinogen deaminase, uroporphyrinogen decarboxylase, and coproporphyrinogen oxidase, also were increased markedly in the Harderian gland and not influenced by AIA treatment. The level of ferrochelatase (FeC) mRNA in the gland was, however, lower than that in the liver. The gland contained an extremely high level of protoporphyrin, while heme was undetectable. Microsomal heme oxygenase-1 (HO-1) mRNA levels were significantly higher in the Harderian gland than in the liver. When isolated glands were incubated with hemin in vitro in organ cultures, the level of HO-1 mRNA was increased, whereas the ALAS-N mRNA level was not. These findings indicate that markedly elevated levels of protoporphyrin and extremely low levels of heme in the Harderian gland are the results of both decreased expression of FeC and markedly increased expression of ALAS-N and HO-1. The constitutive expression of the ALAS-N gene in the Harderian gland suggests a novel transcriptional control mechanism of this gene.
在大鼠的哈德氏腺中研究了δ-氨基-γ-酮戊酸合酶（ALAS）以及其他血红素途径酶的mRNA的表达模式。Northern印迹和原位杂交分析表明，非特异性ALAS（ALAS-N）mRNA在该组织中高表达，而红系特异性ALAS（ALAS-E）mRNA则不表达。对ALAS的免疫印迹分析也在蛋白质水平证实了这一发现。ALAS-N mRNA在哈德氏腺中被最大程度地诱导，并且用2-烯丙基-2-异丙基乙酰胺（AIA）处理动物后其表达不再进一步增加。其他血红素途径酶的mRNA水平，即δ-氨基-γ-酮戊酸脱水酶、胆色素原脱氨酶、尿卟啉原脱羧酶和粪卟啉原氧化酶，在哈德氏腺中也显著增加，并且不受AIA处理的影响。然而，该腺体中铁螯合酶（FeC）mRNA的水平低于肝脏中的水平。该腺体含有极高水平的原卟啉，而未检测到血红素。微粒体血红素加氧酶-1（HO-1）mRNA水平在哈德氏腺中显著高于肝脏。当在器官培养中体外将分离的腺体与血红素一起孵育时，HO-1 mRNA的水平增加，而ALAS-N mRNA的水平没有增加。这些发现表明，哈德氏腺中原卟啉水平显著升高和血红素水平极低是FeC表达降低以及ALAS-N和HO-1表达显著增加的结果。哈德氏腺中ALAS-N基因的组成型表达提示了该基因一种新的转录调控机制。
